The present invention relates to a method of and apparatus for producing an amorphous silicon semiconductor device. More particularly, the present invention is concerned with an improvement in the method of and apparatus for producing an amorphous silicon semiconductor device in which a plurality of amorphous silicon layers having different conductivity types or a plurality of amorphous layers consisting mainly of silicon and having different optical band gaps are successively formed on a substrate, by allowing plasma reaction of a material gas such as silane gas, an impurity gas which determines the conductivity type, e.g., diborane, phosphine or the like, or a silane gas which contains impurity gas, e.g., methane, ethane ethylene, acetylene, german, ammonia, nitrogen, oxygen or a compound of nitrogen and oxygen.
FIG. 7 shows the construction of a photovolatic force device which is a typical example of semiconductor devices making use of amorphous silicon (referred to as a-Si hereinunder). A reference numeral 1 designates a transparent insulating substrate such as a glass sheet on which are successively formed a plurality of layers including a transparent conductive layer 2 such as of indium tin oxide, an a-Si film 3 and a rear surface electrode layer 4 such as of aluminum. The a-Si layer is composed of a p-type layer 5 in contact with the transparent electrode 2, an n-type layer 7 contacting the rear surface electrode 4 and an i-type layer (non-dope layer) 6 intermediate between the layers 5 and 7. These layers 5, 6 and 7 are formed by deposition through plasma reactions of silane gases containing suitable impurities. The term "i-type layer" means a layer which is not doped with any impurity. However, the i-type layer 6 of a-Si may contain a trace amount of impurity because this layer 6 inherently has slight n-type conductivity. The i-type layer 6 also may contain elements of Group IV in periodic table, e.g., germanium (Ge), tin (Sn) or the like, in order that this layer has a reduced optical inhibition band width.
FIG. 8 shows a conventional plasma reaction apparatus which is suitably used for the purpose of forming the a-Si film 3. The apparatus has first to third reaction chambers 10a to 10c which are arranged apart from and in a side-by-side fashion to each other. These reaction chambers 10a to 10c are adapted to be supplied with predetermined reaction gases through first to third valves, respectively. More specifically, a silane gas (SiH.sub.4) and diborane gas (B.sub.2 H.sub.6) are introduced through the first valve 11a, while the second valve 11b is adapted for passing the silane gas. The third valve 11c is adapted to pass the silane gas and a phosphin gas (PH.sub.3). The reaction chambers 10a to 10c are adapted to be evacuated by a vacuum system through fourth to sixth valves. First electrodes 13a to 13c and second electrodes 14a to 14c are disposed in the respective reaction chambers such that the first and the second electrodes in each chamber oppose each other. An A.C. electric field is applied between the first and the second electrodes by means of an A.C. power supply 15. A reference numeral 16 designates a roller conveyor which is interposed between the first and the second electrodes 13 and 14 in each reaction chamber. The conveyors 16 are adapted to be used for conveying the substrate from the first to third reaction chambers. The first to third reaction chambers 10a to 10c have vertical walls 18 which are provided with first to fourth passage windows 17a to 17d formed at the same level and first to fourth shutters 19a to 19d adapted for opening and closing these window passages. The arrangement is such that, when a substrate is from one to another reaction chamber, the shutters are operated to open the desired passage windows.
A conventional method for producing an amorphous silicon semiconductor device employing the apparatus shown in FIG. 8 will be explained hereinunder.
A substrate 1 on which is formed a transparent conductive film 2 alone is moved from the first window passage 17a into the first reaction chamber 10a by means of a roller conveyor 16. In this state, all the shutters 19a to 19d are in closed position, and all the roller conveyors 16 are stopped. In addition, first to sixth valves 11a to 11c and 12a to 12c are closed, and no electric field is applied to the first and second electrodes 13 and 14. Subsequently, the first to third reaction chambers 10a to 10c are evacuated through the fourth to sixth valves 12a to 12c. Thereafter, the first valve 11a is opened so that the silane gas and diborane gas are introduced into the first reaction chamber 10a. Then, an electric field is applied between the first and the second electrodes in the first reaction chamber 10a so as to cause plasma reaction in this reaction chamber 10a. As a result, p-type layer 5 is formed on the transparent conductive film 2.
After the formation of the p-type layer 5, the discharge in the first reaction chamber 10a is stopped and then the gas is purged from the first reaction chamber 10a. Thereafter, the second shutter 19b is opened and the substrate 1 is moved from the first reaction chamber 10a to the second reaction chamber 10b through the second passage window 17b. Then, after the second shutter 19b is closed, the second reaction chamber 10b is filled with silane gas and electric field is applied between the first and the second electrodes 13b and 14b in the second reaction chamber 10b, thereby forming the i-type layer 6. Then, after the gas in the second reaction chamber 10b is purged, the substrate is moved to the third reaction chamber 10c. After the third reaction chamber 10c is charged with the material gas which is the mixture of silane gas and phosphin gas, electric field is applied between the electrodes 13c and 14c thereby forming the n-type layer 7.
As will be understood from the foregoing description, the conventional method and apparatus for producing an amorphous silicon semiconductor device having a plurality of a-Si layers of different conductivity types require the substrate to be moved, after an a-Si layer of a specific conductivity type is formed, from one reaction chamber to another reaction chamber. Before moving the substrate, it is necessary that the material gas is purged from the reaction chamber from which the substrate is to be moved. In addition, it is necessary that the discharge be stopped each time the substrate is moved. In consequence, time is wastefully consumed for the purge of the gas from each reaction chamber, resulting in an impractically large consumption of the material gases. Furthermore, greatest care is required for the handling of the wasted material gases because these gases are generally dangerous. It is to be noted also that, since no specific consideration is given to the spacings between the electrodes in the respective reaction chambers, the film-forming speeds in these chambers are the same. In the case of the production of PIN-type photoelectromotive force device, the i-type layer has a thickness which is about 10 times as large as those of the other layers. This means that the formation of the i-type layer requires a processing time which is about 10 times as long as those required for the formation of the other layers. In consequence, the rate of production of this type of device is limited by the rate of formation of the i-type layer.